Jennie, Naoki, Jenne, Elenna, Vicky
We took more measurements of 40mA vs. 20mA on the OMC SUM DCPD (that is, the DARM offset).
This is because our previous measurements did not correct DARM by the calibration at high frequencies, as the PCAL > DARM broadband transfer functions had low coherence at these frequencies.
The technique above 500Hz is thus to take a DARM ASD spectra and correct it by the peak height of the 1083 Hz PCAL line.
Measurement 1:
21:16:43 UTC
20mA (in OBS), so squeezing injected.
Ref0
Measurement 2:
21:38:42 UTC
20mA (IN COMMISSIONING), no squeezing.
Ref1
Measurement 3:
21:52:24 UTC
40 mA (IN COMMISSIONING), no squeezing.
Ref2
Measurement 4:
22:08:09 UTC
40mA (IN COMMISSIONING), squeezing injected.
Ref3
The measurements are saved in /ligo/home/jennifer.wright/git/DARM_offset/2023-05-05_2114UTC_H1_DARMSPEC.xml.
Attached are the scaled spectra (courtesy of Jenne).
Since the noise looks lower between 40mA no squeeze(brown) and 20mA no squeeze (green), we will go with this offset.
We are not sure why the 40mA, squeezer on trace looks so bad at low frequencies. There's not a way for the homodyne angle to produce the given change in the squeezing blue/pink traces, so that is likely the effect of something else on the squeezing. The most relevant comparison should be the no-squeezed DARM traces at different homodyne angles, green vs. brown.
The pink trace, particularly when you look all the way to low frequency (not shown in this plot), includes a glitch time in it. Not a big deal, since the thing we were looking at here was a lot of the high frequency portion, where the glitch does not seem to be present.